The invention concerns a filter element for separating particles from a particle-laden raw unfiltered gas flow, including a first filter wall having a plurality of first through-flow openings for the entry of the contaminated unfiltered gas, a second filter wall which is arranged downstream of the first filter wall in the flow direction and has a plurality of second through-flow openings for the exit of the clean gas, an intermediate flow space between the first and the second filter walls, wherein the second through-flow openings are arranged in displaced relationship with the first through-flow openings in the flow direction, the second filter wall has at least one impingement wall region so arranged that the particles passing through the first through-flow openings at least partially impinge thereon, and the first and/or the second filter wall is in the form of a wall which is pleated or folded alternately inwardly and outwardly relative to the intermediate flow space, in particular in the form of a folded foil or plate.
Filter elements of the above-indicated kind are known for filtering the outgoing discharge air in painting installations. Those filter elements are based on the operating principle of centrifugal force separation. With that principle, the particle-laden discharge air, that is to say the unfiltered gas flow, passes through the first through-flow openings into the filter element and is deflected by virtue of the displaced arrangement of the second through-flow openings in the intermediate flow space. In that deflection process, the particles in the unfiltered gas flow, which are of a higher density than the unfiltered gas entraining them, cannot follow the flow path and impinge against the impingement wall. The particles adhere to the impingement wall and therefore accumulate in that impingement wall region, whereas the gas flow from which the particles have been removed issues from the filter element through the second through-flow openings, as clean gas.
In the filters of the above-indicated kind, a layer of particles gradually builds up in that way during the period of operation, and after a given period of operation, that layer of particles results in clogging of the filter or an increase in the flow resistance of the filter. In that case, it is necessary to exchange the previously known filters and to replace the contaminated filter element with a fresh filter element.
As the previously known filter elements are used as non-reusable or disposable elements, they are preferably manufactured from inexpensive materials, in particular paper and cardboard. It is known from DE 1 293 004 A to produce such filters from metal, paper, cardboard or plastic films.
A first problem of the known filter elements is that the regularly required exchange or replacement of the filter elements results in an increased waste volume. In addition the regularly required exchange of the filter element causes increased operating costs as it is regularly necessary to replace the old, clogged filter elements with fresh filter elements.
A further problem of the known filter elements is that, particularly when higher value filter materials such as plastics, metals or the like are used, the filters are often bulky, as those higher value materials are also of greater strengths, and as a result, the filter walls can scarcely be deformed or are difficult to deform and the filter element can scarcely be compressed in regard to its volume.
That disadvantage arises in particular in those uses in which a large wall area is to be covered with the known filter elements in order to achieve filtering of even very fine particles with high volume flow, or other similar applications. In such applications, it is necessary for the through-flow openings to be small and for deflection of the gas flow in the intermediate flow region to be implemented as far as possible through an acute angle in order also to provide for effective separation of very fine particles out of the unfiltered gas flow. In regard to such situations of use however, it is desirable both to be able to transport and store the fresh filter elements in a compact packaging volume, and also to be able to dispose of the used filter elements in a compact, space efficient format. Therefore, it is precisely for such large area uses that only filter elements of paper and cardboard are known, as making the filter element from those materials makes it possible to achieve such a reduction in the transportation and storage volume, because of the good elastic deformability of the materials.
A further problem of known filter elements is that they cannot be employed for a wide variety of different applications. Thus, for example in the sector of agricultural operations, in particular in animal husbandry, increasingly tighter emission requirements mean that it is necessary to clean the outgoing discharge air from operating spaces, such as for example stables and sheds. That discharge air is usually considerably dust-laden, and in addition, often carries animal excretions therewith. In the case of known filter elements, that results in rapid clogging and/or a chemical attack on the filter element, which adversely effects operation thereof. In both cases, replacement of the filter elements is required at very short time intervals, so that those known filter elements cannot be used economically in such cases.